use single quotes for uniformity

programs/backup_ver1.py

@@ -28,13 +28,13 @@ if not os.path.exists(target_dir):
     os.mkdir(target_dir)  # make directory
 
 # 5. We use the zip command to put the files in a zip archive
-zip_command = "zip -r {0} {1}".format(target,
+zip_command = 'zip -r {0} {1}'.format(target,
                                       ' '.join(source))
 
 # Run the backup
-print("Zip command is:")
+print('Zip command is:')
 print(zip_command)
-print("Running:")
+print('Running:')
 if os.system(zip_command) == 0:
     print('Successful backup to', target)
 else:

programs/backup_ver2.py

@@ -38,13 +38,13 @@ if not os.path.exists(today):
     print('Successfully created directory', today)
 
 # 5. We use the zip command to put the files in a zip archive
-zip_command = "zip -r {0} {1}".format(target,
+zip_command = 'zip -r {0} {1}'.format(target,
                                       ' '.join(source))
 
 # Run the backup
-print("Zip command is:")
+print('Zip command is:')
 print(zip_command)
-print("Running:")
+print('Running:')
 if os.system(zip_command) == 0:
     print('Successful backup to', target)
 else:

programs/backup_ver3.py

@@ -49,9 +49,9 @@ zip_command = "zip -r {0} {1}".format(target,
                                       ' '.join(source))
 
 # Run the backup
-print("Zip command is:")
+print('Zip command is:')
 print(zip_command)
-print("Running:")
+print('Running:')
 if os.system(zip_command) == 0:
     print('Successful backup to', target)
 else:

programs/backup_ver4.py

@@ -45,13 +45,13 @@ if not os.path.exists(today):
     print('Successfully created directory', today)
 
 # 5. We use the zip command to put the files in a zip archive
-zip_command = "zip -r {0} {1}".format(target,
+zip_command = 'zip -r {0} {1}'.format(target,
                                       ' '.join(source))
 
 # Run the backup
-print("Zip command is:")
+print('Zip command is:')
 print(zip_command)
-print("Running:")
+print('Running:')
 if os.system(zip_command) == 0:
     print('Successful backup to', target)
 else: